It is conventionally known that an active matrix substrate having a plurality of switching elements such as thin film transistors (TFTs) formed on a glass substrate is used for display devices such as a liquid crystal display device, an organic EL display device, and an electrophoresis display device.
In general, in display devices having an active matrix substrate, pixel electrodes are formed in the uppermost layer of the active matrix substrate to increase the aperture ratio of the display screen.
More specifically, a plurality of TFTs, gate lines, source lines, etc. are formed on a glass substrate of the active matrix substrate, and an interlayer insulating film is formed covering the TFTs, the lines, etc. Pixel electrodes are then formed on the surface of the interlayer insulating film.
Having the above configuration, the pixel electrodes on the interlayer insulating film can be formed to spread even to above the gate lines and the source lines, permitting increase in the area of the pixel electrodes. Also, by forming a thick interlayer insulating film by spin coating, it is possible to reduce the parasitic capacitance between the pixel electrodes and the gate and source lines. In this way, a liquid crystal display device that can suppress or reduce generation of crosstalk and has a large aperture ratio can be implemented.
In a peripheral region of the active matrix substrate, an end of the interlayer insulating film exists, and also a plurality of terminals are formed at ends of the lines. To these terminals, which are placed side by side with a predetermined spacing, an IC driver and an external circuit board such as a flexible printed circuit (FPC) are to be mounted.
At an end of the interlayer insulating film, a large step is formed on the glass substrate. Therefore, in the neighborhood of the end of the interlayer insulating film, a resist for patterning the pixel electrodes is likely to fail in sufficient light exposure, causing generation of residues. As a result, residues of a pixel electrode material may be left under such resist residues, and cause short-circuiting between adjacent terminals.
To solve the above problem, Patent Document 1 discloses formation of an organic thin film pattern between terminals. With such an organic thin film pattern, portions of a pixel electrode material located on this pattern can be etched fast, leaving no residue of the pixel electrode material between the terminals.
Patent Document 2 discloses formation of the same insulating film as the interlayer insulating film between terminals. Patent Document 3 discloses a technique where an insulating film for short-circuit prevention covering terminals is formed along an end of an interlayer insulating film.
Patent Document 4 discloses a technique where, while a resist is subjected to excessive light exposure to ensure no resist residue left behind, reflection of the light by lines after having passed through the resist is reduced, thereby to form pixel electrodes properly.
Patent Document 5 discloses a technique where the boundary at an end of an interlayer insulating film has pits and projections as viewed from the normal to the substrate surface, thereby to obtain a mild tilt angle at the end of the interlayer insulating film, and thus suppress or reduce generation of resist residues.
Patent Document 6 discloses an active matrix substrate which, as shown in a plan view of FIG. 18, includes: a gate insulating film 101 formed on a glass substrate; a plurality of terminals 102 placed on the gate insulating film with a predetermined spacing; and an interlayer insulating film 103 formed on the gate insulating film 101 to cover part of the terminals 102.
Projections 104 are formed from an end of the interlayer insulating film 103 to protrude to the gaps between the terminals 102. The tilt angle of the projections 104 with respect to the surface of the glass substrate is smaller than the tilt angle of the projection-free portions of the end of the interlayer insulating film 103. With this configuration, it is intended to ensure no resist residue left on the projections 104, thereby to prevent short-circuiting between the terminals 102 due to a resist residue.